There have been known super abrasive grinding tools having super abrasive grains of diamond, cubic boron nitride or the like as a grinding tool for cutting, shaving and/or abrading a hard-to-grind material such as ceramics, hard metal, heat resisting steel, or high-speed steel.
For example, as super abrasive grinding wheels for surface grinding, external grinding, internal grinding and the like of the hard-to-grind material, there have been known those which have metal-bonded, resin-bonded, vitrified or electro-deposited super abrasive layers and are divided into various kinds according to their shapes, e.g., straight, dish-like, cup-like, with a shaft or a segment grinding wheel, as defined in JIS B 4131 (Diamond or Cubic Boron Nitride Grinding Wheels).
However, in these super abrasive grinding wheels except those having the electro-deposited super abrasive layer, the abrasive grains are embedded in the bond, and there is almost no cutting edge projection, and accordingly, the grinding wheels must be frequently dressed during operation. Further, the metal-bonded and resin-bonded grinding wheels presently in wide use generally have no pore, that is, have no so-called chip pocket. Accordingly they are disadvantageous in that the discharge of cuttings and the supply of coolant cannot be satisfactorily effected, and the abrasive grains and the bond deteriorate due to clogging and heat, thereby lowering the grinding efficiency. Further, the super abrasive grinding wheels generally have high rigidity though there is slight difference among them depending on the material of the bond layer and the base metal bearing thereon the abrasive layer. The grinding wheel having a high rigidity is generally excellent in grinding accuracy but is disadvantageous in that the high rigidity causes chipping and/or fine cracks in the work surface, thereby lowering the quality of the work surface and making the grinding operation difficult. This is especially significant in grinding hard and fragile materials such as ceramics.
On the other hand, in the case of the grinding wheels having the electro-deposited super abrasive layer, the grinding efficiency can be better when the projection of the cutting edges of the abrasive grains from the bond layer is properly controlled. However, since the abrasive layer is of a single layer, as the abrasive grains are consumed to expose the base metal, the grinding resistance increases and grinding efficiency is greatly lowered, thus reducing the service life of such grinding wheels.
As cutting tips, e.g., throw-away cutting tips, there have been known those formed of hard metal, cermet, diamond, cubic boron nitride, alumina, silicon nitride and the like. These throw-away cutting tips are used for cutting steel, special steel and other metals, but it is difficult to cut so-called sintered advanced ceramics such as alumina, zirconia, silicon carbide, silicon nitride, and the like with the throw-away cutting tips. Accordingly, the super abrasive grinding wheels having the diamond abrasive grains described above are presently in wide use for cutting such materials. However, the conventional super abrasive grinding wheels having metal-bonded, resin-bonded, vitrified or electro-deposited super abrasive layers have the drawbacks described above.